This invention relates to the field of automatic data collection (xe2x80x9cADCxe2x80x9d), and more particularly to automatic data collection employing color machine-readable symbols selected from a color symbology.
A variety of methods exist for tracking and providing information about items. For example, inventory items typically carry printed labels providing information such as serial numbers, price, weight, and size. Some labels include data carriers in the form of machine-readable symbols that can be selected from a variety of machine-readable symbologies, such as barcodes, area or matrix codes, and stacked codes. The amount of information that the symbols can contain is typically limited by the space constraints of the label. These symbologies typically rely on patterns of light and dark symbol elements to encode data. For example, barcode symbologies employ patterns of alternating dark elements (e.g., bars) and light symbol elements (e.g., spaces). Information is encoded in the width of the alternating bars and spaces. The use of only two types of symbol elements (i.e., light and dark) limits the amount of information that can be encoded in a symbol of a given length (density).
The use of color and/or shading has been proposed to increase the information density of machine-readable symbols. Such color symbologies have yet to realize significant commercial success, at least partially due to technological problems associated with reading color symbols. Attempts to read color symbols have relied on two-dimensional video charge coupled devices as color image sensors. Such devices read color in sequential steps, limiting such readers to fixed mount reading devices. Fixed mount readers are not practical in a large variety of applications that require mobility, and thus place undue limitations on the use and commercial acceptance of color machine-readable symbologies.
Under one aspect of the invention, a symbol reader employs an optical element having first and second optical axes positioned to image a same portion of a color coded symbol onto two different portions of an image sensor. The reader includes one or more filters to remove or reduce different color portions of the light reflected from the symbol to create color separations at the image sensor. Thus, a yellow colored filter reduces the blue color component from the reflected light so that the image sensor detects the red and green color components. Similarly, a red colored filter reduces the green color component so that the associated image sensor principally detects the red and blue color components. A comparator, such as a microprocessor, programmed general purposed computer, or digital logic circuit, can determine the position and color of the various symbol elements based on image data produced by the image sensors, and decode the color coded symbol.